This study aims to examine the role of the Na+-K+-2Cl-cotransporter in the avian erythrocyte, its impact on cell volume and hemoglobin oxygen affinity by comparing erythrocytes from pigeons maintained in normobaric conditions and those acclimated to hypobaric hypoxia. The degree of cell volume increase mediated by the transporter will be correlated to degree of hypoxia and to levels of catecholamines in the blood. Verification of the identity of the ions moving into the erythrocyte will be conducted; additionally, quantification of glucose and lactate will determine their effectiveness as osmolytes that promote water uptake by the erythrocyte. The impact on hemoglobin oxygen affinity of altered cell volume and ion movements resulting from hypoxia will be analyzed. This will contribute to the long-term objective of determining the effects of hypoxia on oxygen transport functions of the erythrocyte and thus, on the whole animal. This knowledge will aid in understanding conditions of impaired erythrocyte function, perhaps such as sickle-celled erythrocytes, to the extent that certain cellular homeostatic mechanisms are ubiquitous.